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...th the technologies and workloads of the 1990’s. First, they spread information around the disk in a way that causes too many small accesses. For example, the Berkeley Unix fast file system (Unix FFS)=-=[9]-=- is quite effective at laying out each file sequentially on disk, but it physically separates different files. Furthermore, the attributes (‘‘inode’’) for a file are separate from the file’s contents,...

... that of the disk and make it hard for the application to benefit from faster CPUs. They also defeat the potential use of the file cache as a write buffer. Unfortunately, network file systems like NFS=-=[10]-=- have introduced additional synchronous behavior where it didn’t used to exist. This has simplified crash recovery, but it has reduced write performance. Throughout this paper we use the Berkeley Unix...

... make larger file caches possible. This has two effects on file system behavior. First, larger file caches alter the workload presented to the disk by absorbing a greater fraction of the read requests=-=[1, 6]-=-. Most write requests must eventually be reflected on disk for safety, so disk traffic (and disk performance) will become more and more dominated by writes. The second impact of large file caches is t...

... write cost is 1.0. (1) Figure 3 graphs the write cost as a function of u. For reference, Unix FFS on small-file workloads utilizes at most 5-10% of the disk bandwidth, for a write cost of 10-20 (see =-=[11]-=- and Figure 8 in Section 5.1 for specific measurements). With logging, delayed writes, and disk request sorting this can probably be improved to about 25% of the bandwidth[12] or a write cost of 4. Fi...

...and treats them differently during cleaning. We have constructed a prototype log-structured file system called Sprite LFS, which is now in production use as part of the Sprite network operating system=-=[4]-=-. Benchmark programs demonstrate that the raw writing speed of Sprite LFS is more than an order of magnitude greater than that of Unix for small files. Even for other workloads, suchas those includin...

... languages[19]. The cost-benefit segment selection and the age sorting of blocks during segment cleaned in Sprite LFS separates files into generations much like generational garbage collection schemes=-=[20]-=-. A significant difference between these garbage collection schemes and Sprite LFS is that efficient random access is possible in the generational garbage collectors, whereas sequential accesses are n...

... determine: they are at the end of the log. Thus it should be possible to recover very quickly after crashes. This benefit of logs is well known and has been used to advantage both in database systems=-=[13]-=- and in other file systems[2, 3, 14]. Like many other logging systems, Sprite LFS uses a two-pronged approach to recovery: checkpoints, which define consistent states of the file system, and roll-forw...

...write cost of 10-20 (see [11] and Figure 8 in Section 5.1 for specific measurements). With logging, delayed writes, and disk request sorting this can probably be improved to about 25% of the bandwidth=-=[12]-=- or a write cost of 4. Figure 3 suggests that the segments cleaned must have a utilization of less than .8 in order for a log-structured file system to outperform the current Unix FFS; the utilization...

...xamine the most recent portion of the log. The notion of logging is not new, and a number of recent file systems have incorporated a log as an auxiliary structure to speed up writes and crash recovery=-=[2, 3]-=-. However, these other systems use the log only for temporary storage; the permanent home for information is in a traditional random-access storage structure on disk. In contrast, a log-structured fil...

...th and the same read bandwidth as SunOS with the exception of sequential reading of a file that was written randomly.individual disk operations for each block (a newer version of SunOS groups writes =-=[16]-=- and should therefore have performance equivalent to Sprite LFS). The read performance is similar in the two systems except for the case of reading a file sequentially after it has been written random...

...oth of these factors are improving, the rate of improvement is much slower than for CPU speed. Disk transfer bandwidth can be improved substantially with the use of disk arrays and parallel-head disks=-=[5]-=- but no major improvements seem likely for access time (it is determined by mechanical motions that are hard to improve). If an application causes a sequence of small disk transfers separated by seeks...

...he log. Collecting data in the file cache and writing it to disk in large writes is similar to the concept of group commit in database systems[22] and to techniques used in mainmemory database systems=-=[23, 24]-=-. 7. Conclusion The basic principle behind a log-structured file system is a simple one: collect large amounts of new data in a file cache in main memory, then write the data to disk in a single large...

...he Sprite LFS design borrow ideas from many different storage management systems. File systems with log-like structures have appeared in several proposals for building file systems on write-once media=-=[17, 18]-=-. Besides writing all changes in an append-only fashion, these systems maintain indexing information much like the Sprite LFS inode map and inodes for quickly locating and reading files. They differ f...

...he Sprite LFS design borrow ideas from many different storage management systems. File systems with log-like structures have appeared in several proposals for building file systems on write-once media=-=[17, 18]-=-. Besides writing all changes in an append-only fashion, these systems maintain indexing information much like the Sprite LFS inode map and inodes for quickly locating and reading files. They differ f...

...n entire blocks as in Sprite LFS. The Sprite LFS crash recovery mechanism of checkpoints and roll forward using a ‘‘redo log’’ is similar to techniques used in database systems and object repositories=-=[21]-=-. The implementation in Sprite LFS is simplified because the log is the final home of the data. Rather than redoing the operation to the separate data copy, Sprite LFS recovery insures that the indexe...

...d of the log. Thus it should be possible to recover very quickly after crashes. This benefit of logs is well known and has been used to advantage both in database systems[13] and in other file systems=-=[2, 3, 14]-=-. Like many other logging systems, Sprite LFS uses a two-pronged approach to recovery: checkpoints, which define consistent states of the file system, and roll-forward, which is used to recover inform...

...e media made it unnecessary for the file systems to reclaim log space. The segment cleaning approach used in Sprite LFS acts much like scavenging garbage collectors developed for programming languages=-=[19]-=-. The cost-benefit segment selection and the age sorting of blocks during segment cleaned in Sprite LFS separates files into generations much like generational garbage collection schemes[20]. A signif...

...he log. Collecting data in the file cache and writing it to disk in large writes is similar to the concept of group commit in database systems[22] and to techniques used in mainmemory database systems=-=[23, 24]-=-. 7. Conclusion The basic principle behind a log-structured file system is a simple one: collect large amounts of new data in a file cache in main memory, then write the data to disk in a single large...